Processes are known for reclaiming oil from contaminated used oil (sometimes referred to as waste oil).
One such process is disclosed in U.S. Pat. No. 5,271,808, issued Dec. 21, 1993 to Shurtleff. Shurtleff discloses a process wherein an inclined boiler heats the waste oil, vaporizing and driving off lighter hydrocarbons at temperatures of about 650.degree. F. Heavier hydrocarbons and contaminants, amounting to about 10% of the original oil, collect as a sludge in the bottom of the boiler. The sludge drains for disposal. The lighter hydrocarbons are condensed as a reclaimed oil product.
However, Shurtleff's process produces an oily waste which itself requires specialized disposal.
Other methods which can produce a reclaimed oil and an oil-dry contaminant typically involve subjecting the waste oil to thermal pyrolysis.
For example, in U.S. Pat. No. 5,423,891, issued to Taylor, a process is disclosed for the gasification of solids waste. Heat carrier solids (HCS) are first heated and then fed co-currently with hydrocarbon-bearing solids waste through a rotary kiln retort. The solids waste and HCS co-mingle, transferring heat. The resulting temperatures of 1200 to 1500.degree. F. are suitable to thermally pyrolyze the hydrocarbons in the waste. The resultant vapours are extracted for condensation. The retort solids and HCS are discharged from the kiln for recovery of the retort solids and re-heating of the HCS.
In Taylor's system the HCS are continuously circulated in a material handling loop. The HCS is a coarse granular solid which is heated outside the kiln and gives up its heat inside the kiln. Transport of the HCS around the loop involves considerable materials-handling equipment.
In U.S. Pat. No. 4,473,464, issued to Boyer et al., a process is disclosed for treating heavy crude oil. Carbonaceous solids are finely ground for concurrent feed with crude oil to an indirectly heated kiln. Pyrolyzed hydrocarbon vapours are condensed. Coke and carbonaceous solids are screened, ground and recycled outside the kiln. Heat loss to the solids is minimized and the crude oil is preheated to a temperature high enough to balance any temperature loss by the solids.
U.S. Pat. No. 4,303,477, issued to Schmidt et al., discloses co-currently adding a consumable fine-grained reactive solid to a waste material for binding metal and sulfur contaminants during treatment. The reactive solids, such as lime having a grain size typically less than 1 mm, and waste are thermally cracked as they progress through a rotating, indirectly fired kiln. The solids make a single pass through the kiln, the reactive solid being consumed in the process.
Some of the above described prior art processes involve significant material handling challenges in the recycling and conveyancing of large masses of hot, coarse solids. Other processes, which do not recycle hot solids, involve rejection of a portion of the oily waste or irreversibly consume a catalyst.
There is therefore a need for a simplified process for separating contaminants from used oils. It is the objective of the present invention to provide such a process.